1. Field of the Invention
The present invention relates to a high strength aluminum alloy used for forming fins included in a room air conditioner, said alloy being subjected to at least one of a draw forming, a drawless forming and a combination of thereof such as an extension process, a squeezing process, a barring process, a bashing process, or a reflare process for preparation of fins included in a room air conditioner, and also relates to a method of manufacturing the same.
2. Description of the Related Art
In general, an aluminum alloy fin included in a heat exchanger for an air conditioner comprises a plate portion 1 and a collar portion 2 to which a heat exchanger tube is mounted, as shown in FIGS. 1A to 1D. Depending on the shape of the plate portion 1, the aluminum alloy fin is classified into a flat type as shown in FIG. 1A, a roover type as shown in FIG. 1B, a slit type as shown in FIG. 1C, and a corrugation type as shown in FIG. 1D.
FIGS. 2A to 2F collectively show how to apply a draw forming, which is essentially based on an extension process, to an aluminum alloy plate for preparation of an aluminum alloy fin. It is seen that an extension process as shown in FIG. 2A is applied first to the plate portion 1, followed by applying a squeezing process as shown in FIGS. 2B to 2D and subsequently applying a punching process and a barring process as shown in FIG. 2E. Finally, a reflare process is applied to the aluminum alloy plate to form a collar portion 2 as shown in FIG. 2F. Since the draw forming shown in FIGS. 2A to 2F is based on the extension process, the fin material is required to exhibit an excellent elongation. To meet the requirement, used in general is a thick alloy plate material having a homogenizing treatment applied thereto and having a thickness of at least 0.12 mm. For example, O material or H22 material is used in general for forming an aluminum alloy fin. It should also be noted that, in the case of applying a draw forming treatment to a thin aluminum alloy plate having a thickness not larger than 0.115 mm, problems are brought about such as a forming deterioration and an insufficient mechanical strength. Such being the situation, it is very difficult to prepare a fin of a small thickness or to achieve a high collar height-forming of a thin plate material by using alloy materials available nowadays.
For overcoming the problems described above, a drawless forming, which is based on a bashing process, has come to be a main stream in the manufacture of a fin these several years. FIGS. 3A to 3D collectively show the drawless forming technique. Specifically, a punching-hole expanding process as shown in FIG. 3A is applied in the first step to a plate portion 1, followed by applying a barring process as shown in FIG. 3B and subsequently applying a bashing process as shown in FIG. 3C. Finally, a reflare process is applied as shown in FIG. 3D. The drawless forming, which is employed in general for the manufacture of a thin fin having a thickness not larger than 0.12 mm, permits decreasing the thickness of the fin to about 0.115 to 0.105 mm in the low collar height-forming technique.
The material to which the drawless forming is applied requires an excellent bashing workability and a reasonable mechanical strength. In general, semi-hard materials such as H24 to H26 materials are used as the material meeting the above-noted requirements. However, it is still difficult to achieve a high collar height-forming of a thin plate material having a thickness not larger than 0.12 mm by means of the drawless forming. In such a case, it is unavoidable nowadays to use a alloy plate material having a large thickness.
What should also be noted is that, in the case of preparing a pre-coated fin (surface treated fin) by means of the drawless forming technique, a defective forming is derived from the wear of the mold and the molding tool during the pressing process over a long period of time. Naturally, it is necessary to apply maintenance periodically to the mold and the molding tool, leading to a high maintenance cost. Thus, it is strongly desired in this technical field to maintain a high molding capability and to lower the maintenance cost of the mold and the molding tool.
An additional difficulty to be noted is that, in the drawless forming technique, the deterioration of moldability is likely to be brought about in many cases by the decrease in viscosity of the lubricating oil as in the case of using, for example, a volatile oil.
In recent years, a composite forming utilizing the draw forming and the drawless forming in combination has come to be employed in many cases. FIGS. 4A to 4F collectively shows the composite forming technique noted above. In the composite forming technique, an extension process shown in FIG. 4A is applied first to the plate portion 1, followed by applying a squeezing process as shown in FIG. 4B and subsequently applying a punching and barring process as shown in FIG. 4C to the raw material alloy plate. Further, a bashing process as shown in FIGS. 4D and 4E and a reflare process as shown in FIG. 4F are successively applied to the raw material so as to obtain a desired fin.
In the composite forming technique outlined above, a collar portion having a reasonable height is prepared by the extension process and the subsequent squeezing process, followed by applying a bashing process. The particular technique permits diminishing the bashing rate, compared with the drawless forming technique. When it comes to an aluminum alloy plate which is widely used nowadays as a fin material, however, it is still impossible to maintain sufficiently a satisfactory molding capability and to lower sufficiently the maintenance cost of the mold and the molding tool even in the case of employing the composite forming technique.